We are about to purchase batteries for the competition. It is our first competition. How many Robot Batteries, Controller batteries and recharging stations do you guys recommend we get. We currently have one power pack and have found that the battery would last about three match lengths (8 mins) before it starts to be a noticeable change in performance. Is it still good to change the battery after each match?
It was never good to (re)charge the battery after every match.
Figure out how many matches, how much practice, and how many PSC or DSC runs you plan to perform; and then buy the right number of batteries. Remember that they can be recharged during the event and that you might get into the elimination rounds of a tournament/scrimmage.
Battery Power: No team wants to hear the ref or FTA say that their control issues are caused by low battery, especially when the battery just came off charge, but this is a common cause of problems. Measuring voltage with a voltmeter, or the transmitter voltage monitor, is not a sufficient test for battery health, you really need to test for voltage under a load. Ni-Cads have a problem called voltage depression or lazy battery effect. This is caused when a battery is used for only a short time and then put back on charge for a long period, precisely what most teams do after a match. The battery appears to be fully charged but seems to discharges quickly after a brief period of operation. For a more detailed description go to [Nickel–cadmium battery - Wikipedia If your batteries have been around for a while you may want to consider doing a few deep discharges prior to your next tournament.
Blake](Nickel–cadmium battery - Wikipedia If your batteries have been around for a while you may want to consider doing a few deep discharges prior to your next tournament. )
A simple way of testing the battery under a small load is to plug the 7.2V battery into your VEX transmitter. If the voltage can remain over 8 volts for a few seconds then your battery should have enough charge.
Any other ideas of testing battery voltages under a more realistic load ?
I’ve got a simple rig I threw together that uses a 20W/12V Halogen bulb as a load. It puts a 1 to 1.5A load on the battery and lets me read the voltage on my DVM. It has the added benefit that I can immediately tell by the bulb brightness if the pack is close to discharged.